Developing electrostatic latent images on photo-conductive insulating material



Sept' 9 1958 J. L. TREGAY ETAL 2,851,373

DEVELOPING ELECTROSTATIC LATENT IMAGES ON PHOTO-CONDUCTIVE `.IISL'L'IING MATERIAL Filed NOV. 21, 1955 United States Patent @dice DEVELOPING ELECTROSTATIC LATENT llVIAGES N PHOTO-CONDUCTIVE INSULATING MA- TERIAL Application November 21, 1955, Serial No. 548,083 2 Claims. (Cl. 117-17.5)

This invention relates to process and apparatus for developing electrostatic latent images, and more particularly to process and apparatus for applying the developer powder or toner to electrostatic latent images on photoconductive insulating material prior to the fixing of the developer powder to produce the desired print.

Well known electrostatic printing processes comprise first producing a uniform electrostatic charge upon the surface of a photo-conductive insulating material, such, for example, as paper coated with a nely divided photoconductor, e. g., zinc oxide, applied to the paper base as a solution or suspension in a dielectric film-forming vehicle. The vehicle may be a resin solution or suspension, such as a solution of a silicone resin, in a suitable solvent, or a suspension of a polyvinyl acetate resin in an aqueous medium. Further description of the photo-conductive insulating material, it is believed, would serve no useful purpose since the invention is applicable to the development of electrostatic latent images on all photo-conductive insulating materials. The latent image is produced, as is also well known, by exposing the charged surface to a light image thus discharging the portions irradiated by the light rays while leaving the remainder of the surface in a charged condition. The latent image is then developed by applying a developer powder which is held electrostatically to the charged area. This powder is then fixed to the photo-conductive surface, for example, by heat in those cases where the powder is a resin or other material which can be fixed by heat.

Various techniques have been proposed for applying the developer powder to the electrostatic latent image including, for example, a magnetic brush in which magnetically responsive carrier particles and the developer or toner particles are maintained in a loose mass by a magnetic field. This loose mass is swept across the surface bearing the electrostatic latent image to cause the magnetic particles to carry the developer particles into contact with the latent image and at the same time provide an electrostatic charge upon the developer particles by triboelectricity. The electrostatically charged developer particles are retained on the latent image by electrostatic attraction, the density of the developer particles thus retained varying in accordance with the density of the electrostatic charge producing the image. Upon fixing the developer particles, for example, by heat or in any other manner known in the art, the desired print is produced.

Such prior techniques for developing electrostatic latent images have been found objectionable, particularly for small cut sheets, because of the diiculty of holding and moving the sheets while applying the magnetic brush thereover. Other developer techniques proposed, such as oscillating or rocking powder containing receptacles in which a sheet containing a latent image is placed, the receptacle then rocked or oscillated to cause the developer particles 'to move. over the sheet, the excess developer particles then removed and the sheet thereafter withdrawn to permit the insertion of a new sheet containing an elecatented Sept. 9, 1958 trostatic latent image to be developed, are objectionable in that they require excessive handling of the sheets and the developer with consequent waste of labor and time.

It is among the objects of this invention to provide an improved method and apparatus for developing electrostatic latent images or charged patterns, free of the above noted disadvantages of prior techniques.

lt is another object yof this invention to provide a developer apparatus which is simple and compact in design and efficient in operation.

Other objects and advantages of this invention will be apparent from the following detailed description thereof.

In accordance with this invention the developer powder is applied by agitating a mass thereof to maintain it in a loose, uncompacted condition, and the sheets containing the electrostatic latent images are fed through this mass, the particles of which pass over and in contact with the electrostatic latent images and adhere thereto by electrostatic attraction.

The apparatus for practicing this process involves a pair of rotatable feed rolls and a hopper for the developer mix disposed directly above the feed rolls which act as a seal for the base of the hopper. The lower edges of the side walls of the hopper engage the top of the feed rolls to function as scrapers to prevent the feed rolls, in their rotation past the sides of the hopper, from removing dea preferred form of this invention without limiting the claimed invention to this illustrative instance.

Figure 1 is a side elevation partly in section of a developer apparatus embodying this invention. This tlgure is taken in the direction indicated by the arrows associated with line 1-1 on Figure 2; and

Figure 2 is a vertical section partly in elevation taken in a plane passing through line 2 2 on Figure l.

In the drawing 10 indicates a hopper constituted of opposite side plates 11 and 12 and end plates 13 and 14. The side plates 11 and 12 are desirably supported from the standards 15 carried by the frame 16. The end plates 13 and 14 are suitably mounted on the frame 16 through the supports 16'. The base of the hopper is sealed for all practical purposes by a pair of rotating feed rolls 17 and 13 disposed immediately below the hopper so that the of roll 18. Similarly, side plate 12 is individual to and extends in the same longitudinal direction as the axis of two rolls have their peripheries in abutting relation, as shown in Figure 2, thus forming the desired seal for the base of hopper 10 containing a mass of developer mix 19.

The side plates 11 and 12 of the hopper desirably are of thin flexible metal and their base edges act as scrapers to prevent the withdrawal of developer mix by the rolls 17 and 18 during their rotation.

As shown in Figure 1 of the drawing, the rolls 17 and 18 are mounted for rotation in ball bearings 21 on the frame 16. It will be understood that any desired mounting for these feed rolls may be used and that either or both of these rolls may be driven, for example, by la motor (not shown).

The developer mix 19 may be composed of granular carrier particles admixed with pigmented or dyed powder, the granular carrier particles functioning to carry and to generate triboelectric charges on the electoscopic developer powder. Where a negative electrostatic charge forms the latent image, the electroscopic powder and carrier particles should be selected so that the developer powder is triboelectrically positive to the carrier particles. in the event the latent image is constituted of a positive electrostatic charge an electroscopic powder and granular carrier should be selected in which the developer powder is triboelectrically negative to the carrier particles. Preferably, the carrier particles are spherical in shape and may be iron, glass or polyethylene beads having a diameter of approximately .015". The pigmented or dyed developer powder may be a suitable resin, such as vinyl chloride-vinyl acetate copolymers, phenol formaldehyde, Vinylidine chloride resin, butadiene polymers, etc. As noted above, the carrier and the powder are so chosen that they have the desired triboelectric relationship which, of course, will depend on their relative positions in the triboelectric series. It is desirable to select a developer powder and a carrier which when mixed results in a marked electrostatic charge on the developer powder. As such mixtures of carrier particles and developer powders are Well known (being described, for example, in United States Patent 2,618,551) it is believed further description thereof is unnecessary for a full understanding of the present invention.

Positioned above the hopper is a pair of feed rolls 22, 23 one or both of which may be driven. These rolls are mounted for rotation in ball bearings 24 on the frame 16 and are adapted to receive successive sheets 25 from the hopper 10 and feed these sheets having the developer powder thereon to the fixing zone. If desired, feed rolls 22 and 23 may be heated so that xing of the developer powder takes place in the passage of the sheet through these feed rolls.

In operation, as the sheet passes through the developer mix in hopper 10 the carrier particles roll against the sheet and deposit an even coat of developer particles on the charged areas. The agitation of the developer mix by the rotation of the rolls and the passing of the sheet brings a new supply of developer powder into position constantly. As the developer powder becomes exhausted a fresh supply can be added to the hopper 10 manually or otherwise, as, for example, by a shaker, and the mix thoroughly stirred to distribute the powder throughout the granular particles.

Hopper 10 may be of steel or other metal. The rollers 17 and l desirably are rubber surfaced feed rolls. Similarly, rolls Z2 and 23 may be rubber surfaced. It will be appreciated that other materials of construction may be employed, provided the surface of the feed rolls is such as not to damage the photo-conductive insulating material fed thereby.

It will be noted the present invention provides a developer apparatus which is simple in design `and efficient in operation. The process practiced in the operation of this apparatus is free of the objections to the above noted prior developer techniques, particularly in that it is admirably adapted to the successive feed of the sheets including small sheets, and the efficient application of the developer powder to the electrostatic latent images thereon.

Since certain changes in carrying out the above process and in the developer apparatus set forth, which embody the invention, may be made without departing from its scope, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A process of Vdeveloping electrostatic latent images on photo-conductive insulating material, which' process comprises supporting 4a body of carrier particles admixed with developer powder on a pair of abutting rotatable feed rolls, rotatingl said feed rolls to agitate the base of said body and thus maintain said mixture in said body in a loose uncompacted condition and to simultaneously feed said photo-conductive insulating material through the nip of the feed rolls and the agitated body of developer powder so that the photo-conductive insulating material containing said images is contacted by the loose mixture thereby depositing and adhering the developer powder in said mixture to the latent images on said photo-conduc-l tive insulating material, removing the photo-conductive insulating material having the developer powder thus deposited thereon from said agitated body of developer powder and fixing the developer powder on said photoconductive insulating material.

2. A process of developing electrostatic latent images on photo-conductive insulating material, which process comprises supporting a body of carrier particles admixed with developer powder on a pair of abutting rotatable feed rolls, rotating said feed rolls to agitate the base of said body and thus maintain said mixture in said body in a loose uncompacted condition and to simultaneously feed said photo-conductive insulating material through the nip of the feed rolls and the agitated body of developer powder so that the opposite sides of the photo-conductive insulating material are contacted by the loose mixture, thereby depositing `and adhering the developer powder in said. mixture to the latent images on said photo-conductive insulating material, removing the photo-conductive insulating material having the developer powder thus deposited thereon from said agitated body of developer powder and lixing the developer powder on said photo-conductive insulating material.

References Cited in the file of this patent UNITED STATES PATENTS 1,187,008 Nehring June 13, 1916 1,442,129 Cunningham Jan. 16, 1923 2,618,552 Wise Nov. 18, 1952 2,705,199 Clark Mar. 25, 1955 2,761,416 Carlson Sept. 4, 1956 

1. A PROCESS OF DEVELOPING ELECTROSTATIC LATENT IMAGES ON PHOTO-CONDUCTIVE INSULATING MATERIAL, WHICH PROCESS COMPRISES SUPPORTING A BODY OF CARRIER PARTICLES ADMIXED WITH DEVELOPER POWDER ON A PAIR OF ABUTTING ROTATABLE FEED ROOLS, ROTATING SAID FEED ROOLS TO AGITATE THE BASE OF SAID BODY AND THUS MAINTAIN SAID MIXTURE IN SAID BODY IN A LOOSE UNCOMPACTED CONDITION AND TO SIMULTANEOUSLY FEED SAID PHOTO-CONDUCTIVE INSULATING MATERIAL THROUGH THE NIP OF THE FEED ROLLS AND THE AGITATED BODY OF DEVELOPER POWDER SO THAT THE PHOTO-CONDUCTIVE INSULATING MATERIAL CONTAINING SAID IMAGES IS CONTACTED BY THE LOOSE MIXTURE THEREBY DEPOSITING AND ADHERING THE DEVELOPER POWDER IN SAID MIXTURE TO THE LATENT IMAGES ON SAID PHOTO-CONDUCTIVE INSULATING MATERIAL, REMOVING THE PHOTO-CONDUCTIVE INSULATING MATERIAL HAVING THE DEVELOPER POWDER THUS DEPOSITED THEREON FROM SAID AGITATED BODY OF DEVELOPER POWDER AND FIXING THE DEVELOPER POWDER ON SAID PHOTOCONDUCTIVE INSULATING MATERIAL. 